West central Michigan tree fruit update – Aug. 13, 2019

General comments

A quick tart cherry harvest for west central Michigan allowed growers to move through quickly and finish up before things got too ugly, and we're now turning our eyes towards peaches. Early Redhaven and other early fresh market varieties are being harvested now, with earlier processing peach harvest likely to begin sometime next week. Apple harvest is going to be somewhat late this season. Early fresh market varieties currently look to be running at least a week behind, so we will keep an eye on that situation in coming weeks.

Several good rains in the past two weeks have helped to keep soil moisture at acceptable levels in most places. July got dry and mandated extensive irrigation, particularly on young orchards, but we have moved into a span of moderate temperatures with fairly frequent rainfall. More rains are forecasted for the tail end of the week and temperatures look to be staying in the high 70s to low 80s, so this trend is likely to continue for the next several days.

We are much closer to five-year average growing degree day (GDD) accumulations than many of us would have assumed we would be given the slow start to spring, but will continue to be behind through the end of the season at this point. The Michigan State University Hart Enviroweather station is sitting at 2,359 GDD base 42, 2,016 GDD base 45 and 1,495 GDD base 50 since Jan. 1. Our five-year average for that span is 2,546 GDD base 42, 2,188 GDD base 45 and 1,638 GDD base 50.

Crop report

Apples are at terminal bud set in most orchards, although you can find vigorous orchards that are still pushing terminal growth. Trees that struggle to hit terminal bud set in coming weeks will see difficulty with hardening off for winter in fall and can experience winter injury, so if you're seeing blocks that are struggling to stop growing, that should initiate some thinking on your part in the off-season on the fertility regimen the orchard is seeing. Dialing back nitrogen and adjusting the timing of applications to earlier in the season can be particularly helpful in addressing this. You could also consider root pruning to help curb some of the vigor next season.

Lush vegetative growth this season means that fruits in many orchards are shaded by extensive vegetative growth. Fresh market growers should be summer pruning right now to open up canopies and get light on to fruit, particularly fruits in the bottom third of the canopy in high density systems in order to ensure good color development in coming weeks. Tops usually color up pretty nicely for most growers since they tend to be less dense and get sufficient sunlight, but bottoms that have too much big wood and leaf coverage can really struggle without some help. Remember, you're aiming for quality over quantity in the fresh market game and you need that red color more than you need a large pile of yellow fruit. Growers considering row applications of foil to improve color are rapidly approaching the timing for deploying this material in earlier varieties such as Premier Honeycrisp and SweeTango.

Summer pruning can come with some concerns of photo-oxidative sunburn of apple fruits. This type of sunburn frequently occurs when fruits that were not exposed to much sunlight are suddenly in full sun following hedging/pruning, and the damage manifests itself as a bleached look on skin that ultimately turns brown. This type of sunburn can occur any time fruits are suddenly exposed to direct sunlight regardless of ambient temperature, unlike the other two types of fruit sunburn which require significant heat. Intermittent sun with rain showers in the next several days should help newly exposed apples acclimate to light, but sunburn protection materials can be applied for extra insurance.

Growers planning on using ReTain need to start thinking about a game plan, as applications of this product are not far off. This product has a myriad of benefits, including improving fruit finish, delaying harvest, stopping fruit drop, reducing fruit cracking, etc., and is a critical tool, particularly for anyone in the fresh market game. Take a few minutes to read these reminders on ReTain as you decide on your plan this year.

Growers should still be monitoring the sooty blotch/fly speck model for 240 hours since 2 inches of rain have fallen on the last fungicide application. Captan will need to be mixed with a sterol inhibitor or strobilurin fungicide to effectively protect against this disease complex.

Tart cherry harvest is over in west central Michigan. Most growers in Oceana County finished up by the first day or two of August, and Mason County growers were at it until about a week later. Generally, quality of fruit coming out of west central Michigan this season was reported to be outstanding by area processors, so despite a light crop and a tough year for spotted wing Drosophila (SWD), we managed to make it through in good form with what we had. Given the current financial situation with the tart cherry industry, sometimes we have to take these small victories when we can.

Growers weighing their options on post-harvest tart cherry sprays given the current financial market are advised to remember that young trees are going to be particularly devastated by early defoliation, so while keeping leaves through August is important in all tart cherry orchards, young blocks just moving in to their prime can be particularly affected in the long run if they are neglected in the second half of the summer.

Peach harvest is underway for early fresh market varieties, and early processing peach varieties are not far off. This means that the final stretch of brown rot control is upon us. There is a tremendous amount of brown rot inoculum out there this year, so make sure you are keeping a tight schedule and incorporating Captan as a protectant in your sprays. Indar at 12 fluid ounces, Flint Extra and Merivon/Luna Sensation are all viable systemic products, but need to be tank-mixed with Captan to help manage resistance. Captan alone will provide some brown rot control and is a critical part of a good management strategy in peach.

A preventative strategy is critical for brown rot; none of these products work particularly well as a back-action option for the disease. This pathogen is extremely aggressive and develops in infected fruit quickly, so trying to eradicate existing infections with a late spray is not a practical solution for us.

Several folks have asked about trapping for/treating for SWD in peaches. Based on previous research conducted in the area, we generally feel that the only folks who might need to worry about SWD are farm-market style peach producers who are selling melt-in-your-mouth-ripe peach fruits, particularly anyone who doesn't refrigerate peaches prior to or during sale. Processing peach producers don't need to worry about SWD, as previous work has shown these fruits are not infested by SWD. Fresh market producers should focus on timely harvest of fruits, refrigerating any unsold fruit at the end of every day, and avoid leaving fruit on trees any longer than they have to. SWD are no different from other fruit flies in that they will be seen inside of split-pit fruits or hanging out around cracked fruits, but that does not mean that they caused the cracks, splits, rots, etc.

Trapping for SWD in peaches is not worth it for crop scouts for a couple of reasons. First, we already know from our sweet and tart cherry trap line that SWD is out in massive numbers, so there's no sense in trying to determine a "first catch" date in peaches to determine risk like we do earlier in the season for sweet and tart cherries. Unlike most of our insect pests that we trap for, SWD doesn't have distinct generations and only goes from bad worse once it starts to climb in July. Second, we know that the numbers of SWD we catch in traps don't really mean anything in terms of a risk assessment for a grower, especially once we enter the exponential phase of its life cycle. Luckily, fresh market peaches don't really seem to be a prime target and processing peaches aren't susceptible. Save yourself some time during this busy growing season and pull the SWD traps down for the year.

Insect report

We expect the second generation of codling moth to begin flight at around 1,060 GDD base 50 after biofix one, but this was a very challenging year to set a reliable biofix in orchards due to the sporadic nature of flight. It will be important to monitor closely for the emergence of second generation in every block in the coming weeks because flight of the second generation could be equally variable. If you catch a big flight in your trap, you can count start counting to the 250 GDD base 50 mark from that date to time an application, as this will likely coincide with a strong egg hatch.

Timing of treatment for second generation oriental fruit moth is about 200 GDD base 50 after biofix two.

The second generation of obliquebanded leafroller is ongoing; it generally begins around 2,050 GDD base 42 from March 1. We are well past that mark in the region. As with first generation, egg hatch begins 400-450 GDD base 42 after your biofix. Time an insecticide for this mark once you set second generation biofix; treatment is recommended at this time and then at two week intervals for both summer and fall obliquebanded leafroller.

European red mite pressure is building in some orchards, but this has not generally been a banner year for mites. The treatment threshold for European red mites is 10-15 mites per leaf in August.

Products targeting the second flush of San Jose scale crawlers can be timed in the second half of August.

Apple maggot is now active with the recent flush of rains and traps should be out. Use red apple volatile to improve efficacy. The threshold on these volatile baited lures is five per trap.

While we have seen a couple brown marmorated stink bug show up in our traps this season, we did not see any this week and pressure continues to be low.

Japanese beetles continue to be active at this time and activity will be high with the warm weather on the forecast. Be on the lookout for these pests on young trees, as they can skeletonize foliage quickly if left unmanaged.